A typical setting device and method for setting are disclosed by DE 41 26 602 A2. It should be noted that the term "blind rivets" also includes "blind-rivet nuts" unless they are mentioned separately. In the setting of the blind-rivets, a statement disclosing the quality of the connections produced by the blind-rivets is desirable or in many cases even required. It should be ascertained that the blind-rivet was set with the required strength. If the tension utilized to set the blind-rivet was too small, there is the danger that the riveted connection was not produced with the necessary force and will be inferior. If the tension was too large, there is the danger that the material was damaged or in the case of the blind-rivet nuts, that the thread was damaged.
European Patent EP 0 454 890 A1 discloses a power measuring device provided in the device's tension mechanism to assure that the rivet setting device operates with a predetermined tension when utilizing transmitting devices such as electrical, hydraulic, pneumatic or hydraulic-pneumatic setting devices. The power measuring device may be in the form of a tension measuring strip or a pressure box, both of which transform the mechanical pressure to an electrical value. The evaluation and monitoring of the setting process is done electrically by comparing the achieved measured power values with established nominal values in databanks. The disadvantage with this arrangement is that the tension measuring strip or pressure box needed for gathering the data of the forces represent added elements which require additional cabling or wiring costs. Furthermore, these elements must be arranged on the tension mechanism, which makes it necessary to disassemble the elements for daily maintenance of the riveting device, thus increasing maintenance costs. There is also the danger that the measuring devices or measuring lines can be damaged. A number of factors will influence the evaluation of the measuring results when using tension measuring strips. These factors include sizes (diameters), tolerances of the tension device, fluctuations of the coefficient of elasticity of the materials between various finishing stages and temperature influences.
U.S. Pat. No. 5,105,719 discloses a hydraulic riveting device for the positioning of a tool which forms a rivethead in a riveting machine. In this machine, a forming-tool is actuated by a hydraulic cylinder. The hydraulic cylinder is connected to a motor by means of a ball-thread drive which, in turn, is connected to a regulator. The moment created by the motor, as well as numerical values of the motion and the velocity of the motor motion, are entered in the regulator. The regulator simultaneously controls the hydraulic pressure needed for the hydraulic cylinder so that the moment produced by the motor remains zero.
Johannes Vogel describes current-regulator fed DC and 3 phase AC drives in the publication entitled Grundlagen der elektrischen Antriebstechnik mit Berechnungsbeispielen, 4.Aufl., VEB-Verlag Technik, 1989, page 254-257 (Elementary electrical drive technique with computation examples, 4th edition). There are also several examples for feedback of information of current or other regulators.
European Patent EP 0 594 333 A1 describes a setting device for blind-rivets which is monitored during the loading of the motor. After the tension device has achieved a certain value, a moderate load must be attained. If this is not the case, the device is stopped because a problem is suspected.